Radio direction finders



L landa Britishcompany `Application January 31, 1955, Serial No. 485,089

' Claims priority, application Great Britain February. 18, 1954 4 Claims. (Cl. 343-121) This invention relates to radiov direction-tinders and .has for its vmain object to provide improved automatic radio direction finders which will. ascertain and indicate 4rwithout ambiguity and very rapidly indeed the direction .of anincoming signal, even though that signal be of very shortduration.

According to this invention there is provided a radio ldirection iindercomprising two substantially perpendicular parsof spaced aerials, two similar phase Shifters each having two outputs,` one phase shifter being connected bevtweenthe aerials of each pair, means for modulating output signals derived from eachof `said outputs with modu-l lating signals which are all-of the same frequency, the

*'modulatingsignals. applied to the output signals from any two outputs of the same phase shifter being in phasezop position, and 'the modulating .signalsapplied to the outputsignals from any two outputs of a different phase shifter being in quadrature, means for combining the four resultant modulated signals, means for producing a reference wave of the same frequency as that of the modulating signals, and means responsive to the phase relation-between the -combined modulated signals and the reference wave for indicating .the direction of an incoming signal. Thefinvention provides a radio direction nder, the ini dications of which are unambiguous by reason of the fact that the effective polar diagram is of the cardioid type and,'moreover, byreason of theV modulating system emplo'yed ythere is yprovided in effect a vpurely electrical gonirometer which can operate at very high speed without any of Vthe limitations inherent inthe use of a mechanically rotated ygoniometer. Accordingly the direction of an incoming signal of very short duration can be ascertained.

Further it ispossible to embody the invention in circuits `which are free of unwanted resonances so that good impedance matching of the aerials over a wide wave band can be readily achieved without any of the difculties inherent in known arrangements employing mechanically rotated goniometers of the inductive or capacitative type.

For a beter -understanding ofthe invention and to show how the same may be carried into effect reference will now be made to the accompanying drawing which shows in simplified diagrammaticV form a preferred embodiment of a direction nder. v

Referring to the drawing the aerial system consists of two mutually perpendicular pairs of spaced aerials N-S and E-W. These aerials may be for example grounded quarter wavelength aerials or elevated dipoles. Between the aerials of each pair is inserted av phase shifting network 1 or 2, these networks being represented diagrammatically merely as rectangles and being similar. They may in practice be of any convenient known form. There are thus four phase shifter terminals which are marked respectively 3, 4, 5 and 6. The terminal 3 is connected to the control grid 7a of valve 7, terminal 4 is connected to the control grid 8a of valve 8; terminal 5 is connected lCC to the control grid 9a of a yvalve 9; and terminal 6 is be seen the signals applied to the control vgrid 7a of the valve 7 are derived 4from `a cardioid which is in spatial quadrature to that cardioid which supplies signals to the control grid 9a.ofvalve 9 in p hase opposition to the cardioid supplying signals to the control grid Sa of -valve 8. Similarly the signalsapplied to the control grid 8a of the last mentioned valve are derived from `a cardioid which is in quadrature withthat supplying control grid 10a of the valve 10. and in phase opposition to the cardioid supplying signals to the control grid 7a of valve 7.

The valves which lare employed as 'modulating valves may be of any suitable type but are shown for simplicity as screen grid valves with modulating energy applied to the screen grids 7b, 8b; 9b and 10b. This modulation, which Imay be, practically speaking, of as high a frequency as is desired, is applied at terminals 11 through'suitable means `such as modulating transformer 12, the secondary of which is connected between the screen grids 7b and 8b of the valves 7 and 8 (so that Vthese screen grids 7b and 8b are drivenin phase opposition) and also through condensers V13 between the screengrids 9b and ltib of the va-lves 9 `and 10. The condensers 13 constitute simple means (other known means may of course be used) for introducing a phase shift to cause the screen grid 9b andthe screen grid 10b constituting the inputs to the valvesl 9 and l0 to A'be in quadrature respectively with the screen gridASb and-,screen grid 9b constituting the inputs to the valves Sand 9.V

The anodes 7c, 8c, 9c and 110e of the four valves are connected to a common output circuit which feeds through a suitable coupling to a receiver 14, which separates the modulating frequency component and supplies it as one of the inputs to a phase comparison circuit 15. The second input to this circuit isa reference wave of modulating frequency shown as derived from one end of the primary of the transformer 12. The phase comparison circuit may be of any well known kind adapted to provide an output signal representative of the phase relation between the two inputs thereto. This output circuit is applied to any suitable indicator schemati=callyrepre sented as za phase meter 16 which is preferably -marked with incoming signal directions as indicated by the letters NESW in the representation thereof.

It will be seen that the resultant signal in the common anode lcircuit of the four valves is the origin-al` received radio frequency signal with the modulating frequency Asuperimposed thereon, and the phase' relation of the Vmodulating frequency -with reference to a datum phase -will be dependent on, and a measure of, the incoming signal direction.

The depth of the modulation of the radio frequency signal in the common anode circuit is dependent upon the phase shift introduced by the phase shifting networks 1 and Z. The instantaneous polar diagram of the system is of the cardioid type land when it is a true cardioid, modulation is achieved and there is one direction of zero signal strength. For this result the amount of phase shift introduced in each of the phase shifting networks 1 and 2 should be (in terms of wavelength) one and a half times the separation (in wavelengths) of each of the aerials of a pair.

In practice, however, 100% modulation is not necessary and modulation as low as 15% is quite satisfactory, enabling a wide wave band to be covered. A preferred value for the spacing of the aerials of each pair is a little under a quarter of a wavelength. With this value of spacing octantal errors are quite small and the pre- Patented July 15, 17958 ferred value of phase shift introduced by the networks 1 and 2 is a little under three eighths of a wavelength.

Owing to the eicient way in which the radio frequency signals on the aerials are added, the whole system is of good sensitivity, appreciably greater than with a normal Adcock system, while owing to the absence of any mechanically driven goniometer requiring to be tuned, good impedance matching to the aerials is readily achievable.

The electrically produced equivalent to goniometer rotation can be very rapid so that the direction of a very short duration signal is ascertainable. Indeed the eiective speed of rotation can be chosen above the band of speech frequencies so that it becomes a simple matter to separate speech signals from direction finding intelligence.

While I have described my invention in certain preferred embodiments, I realize that modifications may be made, and I desire it to be understood that no limitations upon my invention are intended other than those which may be imposed by the scope of the appended claims.

I claim:

l. A radio direction nder comprising two substantially perpendicular pairs of spaced aerials, two similar phase Shifters each having two outputs, one phase shifter t being connected between the aerials of each pair whereby a phase shift is produced between Ithe signals received by the two aerials of each pair so that the Isignals of each pair of aerials, when combined, provide a cardioid polar diagram of reception, means for modulating output signals derived from each of said outputs with modulating signals which are all of the same frequency, the modulating signals applied to the output signals from any two outputs of the same phase shifter being in phase opposition, and the modulating signals applied to the output signals from any two outputs of a different phase shifter being in phase quadrature, a common output circuit means to apply the four resultant modulated signals to said common output circuit, means for producing a reference Wave of the same frequency as that of the modulating signals, and phase responsive means responsive to the phase relation between the combined modulating signals and the reference wave for indicating the direction of an incoming signal.

2. A radio direction nder as set forth in claim 1, wherein the means for modulating the output signals includes a plurality of valves, `one valve for each phase shifter output, said valves including at least a cathode, an anode, a first control grid and a second control grid,

and wherein the output signals from each phase shifter that the phase relationship of the modulating signals applied to the output signals from any two outputs of the phase shifter are in phase opposition and the modulating signals applied to the outputs of a diierent phase shifter are in phase quadrature, the output of each of said valves being connected in parallel and fed to a common channel.

3. A radio direction finder as set forth in claim 1, including a transformer having primary and secondary windings and wherein the secondary of the transformer is arranged to provide the modulating signals, while the primary of said transformer is arranged to provide the reference wave, and wherein the means responsive to the phase relation between the combined modulating signals and thc reference wave has first and second inputs which are arranged to receive the combined modul-ating signals and the reference wave repectively, and means connected with said phase responsive means for receiving the output thereof and for indicating the direction of an incoming signal.

4. A radio direction finder comprising two substantially perpendicular pairs of spaced polar located aerials, a phase shifting network connected between the aerials of each pair, an output circuit extending from each phase shifting network, a pair of electronic valves individual to each of said output circuits, said valves including at least a cathode, a control grid, an additional grid and an anode, a connection from the opposite terminals of each output circuit to the respective control grids of the pair of valves individual to the yassociated output circuit, a source of applied modulations, means connecting opposite terminals of said source `to the respective additional grids of each of said pairs of valves, means in circuit with the additional grids of one of said pairs of valves for introducing Ia 90 phase shift in the circuits of said last mentioned pair of valves with respect to the other pair of said pairs of valves for eifecting a quadrature relation between the inputs to one pair of valves with respect to the inputs of the other pair of valves, a common output circuit including the anodes of all of said valves in parallel, a receiver connected in said common output circuit, a phase comparison circuit connected with the output of said receiver and with said source of applied modulations and a phase meter connected with the output of said phase comparison circuit for indicating the direction of an incoming signal incident upon said aerials,

References Cited in the le of this patent UNITED STATES PATENTS 2,408,039 Busignies Sept. 24, 1946 2,489,270 Cole Nov. 29, 1949 2,547,028 Libby et al. Apr. 3, 1951 

